This invention relates generally to computers and computing equipment and more particularly to comparators for performing high speed comparison operations.
Traditional devices and methods for comparing two signals, e.g., multi-bit binary signals, A and B, to see if A&gt;B or A.ltoreq.B have relied on some type of adder circuit to determine the difference of B-A. Such an operation would set the carryout signal of the most significant bit to a logical "one" if A was greater than B or a logical "zero" if A was less than or equal to B. The determination of the carryout signal has been deemed essential to ensure that each of the individual bit comparisons provides an accurate and singular output. As will be appreciated by those skilled in the art the operation of determining the carry bit(s) is an inherently serial process in that the carry from the ith bit to the (i+1)th bit is in itself a function of the carry from the (i-1)th bit to the ith bit. This serial characteristic results in time delays, referred to as "carry bit propogation" through the circuitry making up the comparator device.
Inasmuch as one of the basic circuits of a computer or any piece of computing equipment is a comparator, the digital comparison process in state-of-the-art computing is experiencing a high degree of interest for devices and techniques to minimize or obviate the delays inherent in carry bit propogation. To that end techniques have been disclosed to determine the content of each carry bit prior to the operation producing it. Such techniques are frequently referred to as "look-ahead" techniques. However such devices and techniques have not been without some drawbacks, e.g., circuit complexity.
Accordingly, it is a general object of the instant invention to provide a comparator and a method of comparison which overcomes the disadvantages of the prior art.
It is a further object of this invention to provide a comparator and a method for comparing the bits of two, n-bit digital signals without reference to the results of any other bit pair comparisons of those signals.
It is still a further object of this invention to provide a comparator and a method for comparing two, n-bit digital signals in a minimum number of logic levels, independent of n.
It is still a further object of this invention to provide a comparator and a method of comparing two, n-bit digital signals, A and B to determine if A&gt;B or conversly if A.ltoreq.B.
It is still a further object of this invention to provide a comparator and a method of comparing two, n-bit digital signals A and B so that when a conventional comparator for determining of A=B is used therewith, one can determine the following relationships, A=B, A.noteq.B, A&lt;B, A.ltoreq.B, A&gt;B and A.gtoreq.B.